The present invention relates to a device for chilling fresh fruit and other fresh food products and, more particularly, to an improved countertop fruit chiller utilizing a Peltier effect thermoelectric device.
Thermoelectric devices operating in accordance with the well know Peltier effect have been used as cooling/heating devices for many years. Such a thermoelectric device comprises an array of semiconductor couples connected electrically in series and thermally in parallel. The semiconductor couples are sandwiched between metalized ceramic substrates. When DC electric current is applied in series to the thermoelectric device, it acts as a heat pump with heat being absorbed on the cold side, thereby cooling it, while heat is dissipated at the other side. Reversing the current causes the direction of heat flow to be reversed. Attaching a heat sink and a cold sink to the respective hot and cold sides may enhance the efficiency of the thermoelectric device.
Peltier effect devices have long been used to provide coolers and/or heaters for keeping foods fresh or for warming foods for serving. It has also been found and is well known to use forced-air convection to aid in heat transfer. A small electric fan is typically used to circulate air past the cold sink and into and through a container for the food, while another fan moves ambient outside air across the heat sink to dissipate heat from it.
Although chillers for fresh fruit and other perishable food products are well known in the art, the market success of such devices has been limited. There appear to be a number of reasons for this lack of market success. One is the cost and heat transfer efficiency of the solid state thermoelectric modules. In addition, the need to provide circulation of cool air to attain the greatest cooling efficiency has led to complex duct systems which add substantially to the cost of the containers, typically made of molded plastic materials. Another issue with prior chillers is the distribution of the cool air amongst the food to be chilled. It is well known that the mixing of various velocity airflows produces a turbulence that leads to improved overall distribution of the cold air thus improving the overall cooling efficiency.
In accordance with the present invention, a chiller for fresh fruit or other perishable food products utilizes a construction which optimizes a cooling air flow and thus heat transfer efficiency with a container construction that is less expensive to manufacture and permitting the use of a relatively smaller thermoelectric module. Thermoelectric modules of increased efficiency, such as disclosed in U.S. Pat. No. 5,448,109 is particularly suitable for use in the fruit chiller of the subject invention.
In its broadest aspect, the food chiller of the present invention comprises a base housing for mounting a Peltier effect thermoelectric module sandwiched between a cold sink and an opposite heat sink. The housing, together with a baffle plate and an inner bowl or food container, also defines a duct system that includes a cool air supply duct in heat transfer communication with the cold sink, a return air duct, and a cool air circulation fan in the cooling duct system to circulate air therethrough.
A food container portion is adjacent the base housing and contains an enclosing sidewall and a removable or openable cover for retrieval of the food. The food container portion has therein a plurality of outlet holes and an inlet slot that communicate with the duct system.
The airflow inlet slot allows air to enter the food container around the upper periphery of the food container. Generally centrally located outlet holes in the lower portion of the food container return the air to the cooling duct and cold sink. The cross sectional area of the airflow inlet slot varies in size. This variation of cross sectional area produces variations of the velocity of the inlet airflow. When the airflows of various velocities mix, turbulence results and improves the mixing of the air within the food container.
The food container portion is normally closed with a removable or openable cover such that cooling air is continuously recirculated. In one embodiment, however, an outside ambient air supply conduit communicates with the cooling duct system and includes a metering device to admit a controlled flow of outside air to assist in purging the cooling duct system of ethylene gas and other ripening by-products of fruit. The metering device may comprise a small diameter tube connected to the duct system upstream of the fan.
To help maintain the interior temperature of the container, a removable insulating sleeve may be inserted into the container. The sleeve is shaped to conform to the interior of the enclosing sidewall. The removable cover may also be provided with an insulating liner.
Various arrangements of partitions may be placed within the container to divide the container into different temperature zones by varying the flow of cooling air through the zones. Such partitions may be vertically disposed to extend upwardly from the container bottom wall or may be horizontally disposed and attached, for example, to a central tower or to the container sidewall.